Ben Spies boosted his fastest lap in Austin by more than four seconds at the end of free practice on Friday to see out the opening day in 10th place.

The Ignite Pramac Ducati rider managed to keep the CRT machines of Aleix Espargaro and Yonny Hernandez at bay with a time of 2m 08.034s on his satellite Desmosedici, finishing 0.335s behind Nicky Hayden in ninth place on the factory Ducati.

Texan Spies was in positive mood after the first day at the Circuit of the Americas and the former factory Yamaha rider was encouraged to close the gap to Hayden.

"It was a good day. We changed the bike quite a bit in the second session, and I got the feel of it and closed the gap to the factory Ducatis," he said.

"I got some laps in, and now we've got some good data to look at.

"We'll try to take another couple of steps for tomorrow if the track gets better, and just keep closing the gap to the front guys."

Pramac's Andrea Iannone on the Energy T.I. machine was 15th.